Field
This disclosure relates to negative electrodes for secondary batteries and a method of manufacturing the negative electrodes for secondary batteries, and more particularly, to negative electrodes for the lithium secondary batteries and methods of manufacturing the same.
Description of the Related Technology
Lithium secondary batteries are widely used in portable electronic devices such as cell phones, and notebook computers. Demand for lithium secondary batteries is expected to dramatically increase in the future due to continuing development of electronic devices. As a result, lithium batteries having better performance than conventional lithium batteries are of interest due to the increase in demand.
In general, carbonaceous materials having low electric potential such as carbon and graphite are used as negative active materials. However, a theoretical electrical capacity of the carbonaceous materials is only 372 mAh/g. As a result, new negative active materials are of interest for manufacturing high capacity batteries.
For example, silicon is considered as a next generation negative electrode material capable of replacing the carbonaceous materials as a negative electrode material for a negative electrode of a lithium secondary battery. Silicon has an advantage of high theoretical capacity of 4200 mAh/g, which is about 10 times greater than the carbonaceous materials.
However, a negative electrode including silicon may have a change in volume to about 400% during formation and disassembly of a lithium-silicon alloy. Accordingly, capacity of the battery dramatically decreases during a charge and discharge cycle such that a capacity of the battery after a fifth cycle is only 300 mAh/g, which is about 10% of an initial capacity.
A negative electrode including silicon is subjected to high structural stress due to repetitive changes in volume through a continuous charge and discharge process which may lead to cracks and disassociation of parts of the negative electrode from a current collector. As a result, a negative electrode including silicon may be mechanically very unstable. In this regard, parts of the negative electrode where cracks occur decrease electrical contacts between the particles included in the lithium secondary battery, thereby increasing contact resistance. Also, the lithium ions of dissociated parts from the current collector remain isolated and do not participate in an electrode reaction, thereby decreasing cycle performance of the battery.
Recently, manufacturing silicon into a three-dimensional nanostructure such as a nanowire or a nanotube has been investigated as describe in Song, T. et al. Nano Lett. 2010, 10, 1710 in order to potentially solve problems mentioned above. However, there is a structural limitation in achieving a high capacity battery because most of the silicon nanostructures are grown to have an irregular arrangement. Also, the silicon nanostructures are typically manufactured by using a bottom-up method including a high temperature chemical growing procedure which may be cumbersome and increase manufacturing costs.